As to the silicon epitaxial growth methods, the H--Si--Cl type chemical vapor deposition (CVD) process has been most widely studied at present and put in practical applications. The process is such that a silicon source gas is supplied by means of a hydrogen carrier onto a silicon substrate heated to an elevated temperature and a silicon single crystal is deposited and grown on the substrate through the reaction of the H--Si--Cl vapor. The common silicon source gases are SiCl.sub.4, SiHCl.sub.3, SiH.sub.2 Cl.sub.2 and SiH.sub.4.
Various types of furnaces have heretofore been used as the growth furnaces for effecting such epitaxial growth. For instance, single wafer type apparatus may be mentioned as the ones which are meritorious for the realization of semiconductor wafers of greater diameter. This type is designed so that a substrate is loaded on a susceptor within a chamber heated by a radiation heating system using halogen lamps and a reaction gas is supplied into the chamber. Owing to the single wafer processing, this type has the effect of not only making the chamber more compact but also simplifying the designing of heating conditions, gas flow distribution, etc., and ensuring higher uniformity of the epitaxial film characteristics.
Thus, the above-mentioned conventional epitaxial growth methods and apparatus are all such that after wafer substrates have been heated in a reference gas atmosphere, e.g, hydrogen atmosphere while being loaded on susceptors in a chamber, a source gas is newly released into the reference gas and supplied onto the wafer surfaces thereby producing a reaction gas consisting of a mixture of the reference gas and the source gas and starting the growth.
However, in accordance with the above-mentioned method of heating from one side, i.e., the heating from the back side by the heat conduction from the susceptor, a temperature difference is caused between the surface and back sides of the semiconductor wafer. The occurrence of such temperature difference between the sides of the wafer causes a greater thermal expansion of one side than the other side thereby causing warpage and hence temperature variations in the radial direction of the wafer. This thermal stress tends to result in a slip in the crystal and irregularities in the wafer surface thus leading to the occurrence of defects due to the so-called crystal slip.
Thus, in order to avoid such temperature difference between the sides of a wafer tending to cause a warp or slip defect in the wafer, there has been proposed a method of performing a radiation heating by lamps from the sides of a wafer and this method is not practical since it tends to make the apparatus greater and more bulky.
On the other hand, in the case of the epitaxial growth furnace, a silicon source gas which is supplied along with a reference gas, e.g., hydrogen gas into the furnace reaction chamber toward the surfaces of semiconductor wafers, is also caused to flow along the inner wall surface of the chamber thus causing deposition of a silicon product due to the reaction gas on the inner wall surface of the chamber. While the reaction chamber wall is generally made from quartz, as the silicon deposit on the chamber inner wall surface accumulates, the chamber wall is shielded from light and also the amount of radiant heat irradiated from the heating means and transmitted through the chamber wall is varied and decreased with time thereby giving rise to the danger of failing to maintain uniform the heating temperature of the semiconductor wafers disposed within the chamber and failing to effect the desired satisfactory epitaxial growth.
In addition, such deposit has the danger of causing variations among different semiconductor wafers even in the case of the epitaxial growth under the same conditions and also causing the deposit in the chamber inner wall surface area located above the semiconductor wafers to fall on the semiconductor wafer surfaces and result in the occurrence of defects when it peels off the wall. Thus, there arises the need for the removing operation of the deposit on the inner wall surface prior to the loading of semiconductor wafers into the chamber. Thus, the deposit on the chamber inner wall surface requires extra time and labour for the maintenance of a given quality for wafers and prevents improvements in the operating efficiency and productivity.
In view of the foregoing deficiencies, it is the primary object of the present invention to obtain an excellent epitaxial growth furnace capable of excellent epitaxial growth of films on the semiconductor wafer surfaces without causing any defect. It is thus an object of the invention to provide an epitaxial growth furnace so designed that when heating the semiconductor wafers during epitaxial growth, despite its simple construction, the temperature difference caused between the sides of the wafers can be considerably reduced than previously and also not only the deposition of a silicon product on the chamber inner wall surface can be prevented but also redeposition of the silicon product on the semiconductor wafer surfaces can be avoided.